Dense flow shot cleaning



July 25, 1961 w. M coLL 2,993,681

DENSE FLOW SHOT CLEANING Filed July 2, 1957 4 SheetsShee'b 1 INVENTOR.Wilham Mc Coll BY w WM ATTORNEY 4 Sheets-Sheet 2 INVENTOR.

William Mc Coll AT TORNEY W. M COLL DENSE FLOW SHOT CLEANING FIG.2

I u l l l l h-HI I H T J 4 6 I 4 6 l I I l I rr I July 25, 1961 FiledJuly 2, 1957 F1-- li w a July 25, 1961 w, MccoLL 2,993,681

DENSE FLOW SHOT CLEANING Filed July 2, 1957 4 Sheets-Sheet 3 34 FIG. 3

INVENTOR. William Mc Coll ATTORNEY July 25, 1961 w, MCCQLL 2,993,681

DENSE FLOW SHOT CLEANING INVENTOR.

William McColl AT TORNEY United States Patent 2,993,681 DENSE FLOW SHOTCLEANING William McCall, London, England, assignor to The 'Babcock &Wilcox Company, New York, N.Y., a corporation of New Jersey Filed July2, 1957, Ser. No. 669,638 Claims priority, application Great BritainJuly 4, 1956 7 Claims. (Cl. 2571) This invention relates to a method ofand apparatus for cleaning surfaces of heat exchange elements in anupright gas pass. The method to which the invention relates is that inwhich solid cleaning particles are dis charged into a gas pass above thesurfaces in the pass to be cleaned. One form of apparatus for carryingout such method is described in British Patent No. 745,556 and includesa plurality of solid cleaning particle scattering means which are spacedfrom one another and positioned above the heat exchange surfaces inparticle distributing relation with respect thereto and each of whichincludes a deflector and means-for directing a stream of particlestowards the deflector, collecting means for collecting the particles ata location below the pass and conveying means adapted to convey theparticles from the collecting means to an elevation above the scatteringmeans. In the operation of the apparatus the particles during thecleaning period are continuously circulated by pneumatic conveyance froma storage hopper below to a separator and distributor above the pass.

In the practice of the said method various difficulties are liable toarise. For example, when the particles are discharged at the ratesnormally adopted and dictated by the capacity of the conveying means tocirculate the particles or/and by the nature of the scattering means, inthe event of the heat exchange surfaces having heavy deposits thereon,then large quantities of particles are liable to be captured by thedeposits on the surfaces without eflectively cleaning the surfaces, withthe result that, as has been found to occur in some installations, thewhole charge of particles in the system is liable to disappear andremain in the gas pass. We have discovered that this danger may largely,if not wholly, be avoided by maintaining over a suitable period a muchdenser discharge of particles than has normally been used.

Another difliculty arises more particularly in connection with gaspasses of large cross-sectional area provided below with a plurality ofhoppers. When in such a gas pass each hopper has associated therewithconveying means arranged to convey particles to scattering meansdisposed above the hopper, a drifting of particles from one circulatingsystem to another tends to occur'and to give an uneven distribution ofparticles between the storage means respectively associated with anddisposed below the hoppers.

Further difliculties to be feared are Wear in certain parts of theconveying means when, as is convenient, pneumatic conveyance of theparticles is adopted, and choking of parts of the collecting andconveying means occurs.

The present invention includes the method of cleaning surfaces of heatexchange means in an upright gas pass by discharging solid cleaningparticles into the pass above the said surfaces, according to which theparticles are elevated by conveying means to storage means to establisha charge of particles in the storage means and particles are dischargedfrom the storage means into the gas pass at a rate much greater than themaximum rate at which the conveying means are able to elevate theparticles.

Advantageously, in order to minimize the requisite storage capacity orto enhance the cleaning effect, during the discharge of particles theconveying means are simulice taneously operated to elevate particlescollected at the bottom of the pass to the storage means.

The invention also includes apparatus for cleaning the surfaces of heatexchange means in an upright gas pass including cleaning particlescattering means positioned above the heat exchange surfaces and adaptedto distribute particles in respect thereto, particle collecting meansincluding a plurality of collectors disposed below respective parts ofthe gas pass and conveying means adapted to convey particles from thecollecting means to a common hopper located at an elevation above andarranged to supply particles to the scattering means. With sucharrangement the danger of segregation of the available particles inrelation to a section or sections of the gas pass is avoided.

The invention furthermore includes apparatus for cleaning the surfacesof heat exchange elements in an upright gas pass including a pluralityof solid cleaning particle scattering means which are spaced from oneanother and positioned above the heat exchange surfaces in particledistributing relation with respect thereto and each of which includes adeflector and means for directing a stream of particles towards thedeflector, collecting means for collecting the particles at a locationbelow the pass and conveying means adapted to convey the particles fromthe collecting means to an elevation above the scattering means, whereinstorage hopper means are arranged to receive the particles from theconveying means and to supply under the action of gravity particles withwhich they are charged to the distributing means and cut-off valve meansare provided for permitting or preventing the flow of particles from thehopper means.

The invention will now be described, by way of ex ample, with referenceto the accompanying diagrammatic drawings, in which:

FIGURE 1 is a schematic side view of an arrangement of apparatus forcleaning surfaces of heat exchange means in an upright gas pass;

FIGURE 2 is a schematic end view of the arrangement shown in FIGURE 1;

FIGURE 3 is an enlarged view of part of FIGURE 1 showing cleaningparticle collecting and entraining means and part of the conveyingmeans;

FIGURE 4 is an end view of the particle collecting means shown in FIGURE3;

FIGURE 5 is an enlarged view of part of FIGURE 1 showing a cleaningparticle separating means including a storage hopper and leading toparticle distributing means; and

FIGURE 6 is an end View of the particle separating means shown in FIGURE5 with part of the separator casing removed.

In the arrangement or FIGURES 1 and 2 an upright gas pass 1 containsbanks 2, 3, 4, 5 and 6 of horizontally extending economizer tubes. Thegas pass 1 is of substantial width and is formed at its lower end withthree hoppers 7 arranged side by side to provide a bottom to the gaspass. Adjacent the gas pass 1 and extending parallel thereto is a gasoutlet pass 8 communicating at its lower end with the economizer pass 1and leading at its upper end by way of an outlet passage 9 to a stack ordraft fan (not shown).

The arrangement is adapted to operate with the flow of hot gasesdownwardly through the upright pass 1 and over the banks 2 to 6 ofeconomizer tubes, and upwardly through the pass 8 as is shown by thearrows 11 after having turned in a gas turning space above the hoppers 7as is shown by the arrows 10. The gases flow from the pass 8 outwardlythrough the outlet passage 9 as is shown by the arrows 12.

The Wall separating the downflow pass 1 and the upflow pass 8 isprovided at its lower end with a downwardly inclined bafiie 38 inwardlyextending with respect to the gas pass 1 and helping to prevent thepassage of particles with the gases into the pass 8 as is explainedhereinafter.

Disposed below the gas pass 1 and cooperating with the lower ends of thehoppers 7 are respective cleaning particle collecting means 13 which areshown more clearly in FIGURES 3 and 4. Thus there are three collectormeans 13 disposed belovt respective hoppers of the gas pass 1 which aresimilarly constructed and arranged. Each collector means 13 comprises abin including an upper part 13' and a lower part 13", the upper part 13being closed by a cover plate 15 disposed at such an angle that when theplate 15 is in cooperation with the bottom of the associated hopper 7the bin of the collector means 13 has an upright position. Each hopper 7is provided with a restricted particle inlet to the collector means inthe form of a slot 20 extending across the width of the associated coverplate 15.

The upper part 13' of each collector means 13 is provided with anassociated downwardly inclined inlet passage 14 for the intake ofwinnoWing gas, suitably atmospheric air, under suction. The inletpassage 14 is adjustable by means of a rotatable closure plate 16pivoted at 17 to control the intake of air therethrough.

' The upper part 13' and the lower part 13" of each collecting means 13are connected by cooperating flanges formed on the respective parts toprovide the bin of the collecting means. The lower part 13 has a slopingbottom 39 leading to a cleaning particle outlet at its lower end formedin a corner of the bin. The slope of the bottom 39 is such that inoperation cleaning particles flow down the slope to the bottom outletwhich is in the form of an outlet spout 27 projecting into the casing ofa cut-oil valve 28 disposed below the collector means.

Within the bin of the collector means 13 is disposed an inclined screen25 for the retention of foreign bodies, such as displaced heat exchangerdeposits, of relatively large size and the screen is spaced a shortdistance above the sloping bottom 39 to limit the length of particles orbodies able to pass therethrough. A side by-pass passage 23 leads froman intermediate region of the bin above the screen 25 to an inlet 26opening to the space between the screen 25 and the bin bottom 39. Anauxiliary screen 24 of similar mesh size to the screen 25 is disposedacross the inlet to the by-pass passage 23 a short distance from theside thereof in order to limit the length of particles or bodies able topass therethroughp The lower part 13 of the collector means is providedwith an access door 22 covering an access opening sufiiciently large topermit removal of the screens 24 and 25.

The cut-off valves 28 respectively disposed below the three collectormeans 13 are suitably of the nature disclosed in the completespecification of British Patent No. 746,620. Each valve includes acup-like member 28' mounted on a pivoted arm and having a closed or flowrestricting position 28" (shown in broken lines) in which the cup isdisplaced from the line of discharge of the spout 27' by rotation of thecup 28' about its pivot. The cup 28' is provided with an upstandingpoker 27 adapted to enter the spout 27 when the cup is in its closedposition.

The casing of each cut-ofl? valve 28 opens at its lower end toassociated entraining means comprising a mixing nozzle device 29 forefiecting entrainment of cleaning parholes in gaseous conveying mediumsuitably air under pressure supplied to the mixing nozzle 29 throughsupply conduit 30. The valve casing is formed with a top opening givingaccess to the valve cup 28' and to the particle inlet to the mixingnozzle device 29. Suitably the top opening is provided in a horizontalcover plate of the valve disposed at a level above the valve cup 28" sothat such access enables attention to be given to the valve and afiordsmeans for clearing any obstruction at the inlet aperture of the nozzledevice 29 even when the particle level in the bin of the collector means13 is above the level of the screens 24 and 25.

As is shown in FIGURES 2 and 3, there are three mixing nozzles 29supplied with air under pressure by a conduit 30 suitably provided atlowermost points below the respective mixing nozzle 29 with drain plugs31 for the removal of stray cleaning particles from the air supplyconduit.

Each nozzle device 29 is in the form of a venturi with the inlet fromthe associated cut-01f valve located at the venturi throat. Each nozzledevice 29 is upwardly inclined towards its discharge end and arranged todischarge entrained cleaning particles into associated conveying meansincluding a straight length of pipe 32 extending parallel orsubstantially parallel to a sloping side of the associated hopper 7. Thepipes 32 are respectively joined by readily replaceable pipe bends 33 toupright pipe lengths 34 leading upwardly to separating means including acleaning particle separating chamber 44 providing a common storagehopper, as is shown most clearly in FIGURES 5 and 6. Thus conveyingmeans extend with a single bend from a particle receiving point at theventuri throat adjacent the collecting means 13 to the storage hopperand separating chamber 44. The provision of a single bend in eachconveying means restricts most of the wear due to the conveyance ofentrained cleaning particles to a single part of the pipe which isreadily replaceable.

Separating means including a separating chamber 44 as shown in FIGURES 5and 6 and described below, form part of the subject matter of acopending application, Serial No. 671,178, filed July 11, 1957, nowPatent No. 2,954,843, granted October 4, 1960. Suitably the separatingchamber 44 is disposed adjacent a main gallery and includes a storagehopper provided by a hopper bottom 46 to the chamber. The hopper bottom46 is formed'with a downwardly directed particle outlet 48 provided atits lower end with a shut-oil valve 53 so that the hopper bottom servesas a storage chamber for cleaning particles which may be dischargeddownwardly therefrom by opening the valve 53. The separating chamber isprovided in a side wall with a hinged door 61 giving access to theseparating chamber.

The separating chamber 44 is provided with a roof 45 formed with impactmeans comprising particle receiving pockets 46' associated with theconveying means from the mixing nozzles 29 and closed at their upperends by impact plates 42. Thus there are provided three upright pockets40 extending partly above and partly below the roof 45 and open at theirlower or inlet ends 43. The pockets 40 are co-axially arranged withrespect to the associated upright ducts 34 of the conveying means, whichextend upwardly through the floor 48 of the chamber 44 with their upperends disposed above the floor and spaced from the associated pocketinlets 43.

Adjacent the pockets 40 in the roof 45 of the separating chamber 44is'formed an opening for the discharge of conveying medium from thechamber. The opening is connected to an outlet duct 47 extending atfirst upwardly and parallel or substantially parallel to the pockets 40and communicating at its end remote from the separating chamber 44 withthe gas outflow passage 9 from the gas pass 8, shown in FIGURE 1. Theoutlet duct 47 is arranged to discharge downwardly into the passage 9immediately above the pass 8.

The single storage hopper provided by the separating chamber 44 isarranged to discharge to a distributor from which respective tubes forthe conveyance of cleaning particles under gravity lead to scatteringmeans. Thus below the outlet 48 from the separating chamber 44 isdisposed distributing means comprising a distributing chamber 49 inwhich is located a cut-0E valve 53 for controlling the flow of cleaningparticles under gravity from the hopper bottom of the separating chamber44 into the distributing chamber.

Suitably the cut-oil valve 53 is of the nature disclosed in BritishPatent No. 745,620 and is power operated and remotely controlled withits movable valve member be- 5. ing gravity biased to a closed or flowrestricting position. Formed in the bottom of the chamber of thedistributing means 49 immediately below the outlet 48 from theseparating chamber 44 and its associated cut-ofi valve 53 is an impactplate 61 providing a horizontal or substantially horizontal impactsurface. A downwardly directed duct 50 providing a particle inlet chuteclosed at its upper end by a hinged closure member 51 extends from aside wall of the distributing chamber 49 and communicates at its lowerend therewith.

symmetrically disposed around the impact plate 61 and opposed to thecleaning particle outlet 41 from the separating chamber are a pluralityof outlets for the conveyance of cleaning particles to scattering means.Thus, there are six outlets 62 respectively communicating withdownwardly directed discharge tubes 52 by way of-fianged connections 56.Below the flanged connections 56 the pipes 52 are bent inwardly towardsthe gas pass 1 and pass in downwardly inclined manner across the upflowpass 8 into the gas pass 1 where they are directed vertically orsubstantially vertically downwardly. The lower or discharge ends 57 ofthe tubes 52 are disposed at intervals across the gas pass 1 as shownin, FIGURE 2 and are provided with respective scattering means 59. Thescattering means 59 are suitably of the nature disclosed in BritishPatent No. 745,556 and each includes stationary deflector means 58supported by and spaced from the outlet end 57 of the associated tube 52by spacers 60. Thus the ends of the tubes 52 provide upright spouts fordirecting cleaning particles downwardly onto the associated impact ordeflector plates 59 which are adapted to effect scattering of thecleaning particles. Suitably the impact or deflector plates 59 of thescattering means are so designed and spaced that the regions served byadjacent scattering means overlap, and the scattering means are suitablyspaced a short distance above the uppermost tube row of the topeconomizer tube bank 2.

The tubes 52 are provided throughout their lengths, which extend throughthe gas upflow pass 8 and the downflow pass 1, with protective jackets.Thus each tube 52 is provided with a co-axial jacket or sheath tube 54of larger internal diameter than the external diameter of the tubes 52.At its outer end the jacket tubes 54 extend outside of the gas pass 8and are fastened to the associated tubes 52 as is shown most clearly inFIGURE 5. A plurality of circumferentially distributed inlet openings 55are formed in the outer end of each of the tubes 54 outside the gas pass8 and communicating with the atmosphere. The inner ends of the jackettubes 54 are open to the gas pass 1 immediately above the associatedscattering means 59 so that in operation owing to the gases flowing inthe pass 1 being below atmospheric pressure, suction within the gas passinduces a flow of cooling air through the jackets 54 by way of theassociated openings 55 and suflicient flow of air is maintained toprotect the tubes 52 from overheating.

,In service, whena cleaning operation is to be initiated, the storagehopper 'of the separating means 44 will normally be fully charged withthe level 64 of cleaning particles just below the upper or outlet endsof the upright conveying pipe lengths 34. After a fan for supplyingconveying air through the conduit 30 to the mixing nozzles 29 has beenstarted, the cut-01f valves 28 at the outlets 27 from the collectormeans 13 are opened so that any dust or cleaning particles collected inthe collector means 13 since the last cleaning operation are conveyed tothe separating chamber 44 where the cleaning particles are retained andthe air and dust are discharged through the outlet duct 47 into theoutlet passage 9. At this stage the power operated remotely controlledcut-off valve 53 is opened and the charge of cleaning particles in thestorage hopper 44 begins to flow under the action of gravity and insubstantially unimpeded manner by way of the distributing means to thesix-scattering means 59 disposed above the economizer tube {banks 2 to6.

Within the distributing chamber 49 the falling cleaning particlesimpinge upon the impact plate 61 where they are scattered sidewardly andpass under the action of gravity downwardly through the outlets 62 tothe conveying tubes 52 as shown in FIGURES 1 and 2 by the arrows 67. Thecleaning particles fall through the tubes 52 and are discharged throughthe upright discharge spouts which form theends of these tubes onto thedeflector 58 of the scattering means 59 where they are scatteredsubstantially uniformly across the gas pass 1 as shown by the brokenlines 63. Deposits on the tubes of the economizer banks 2 to 6 aredislodged by the cleaning particles and fall with the cleaning particlesto the hoppers 7 forming the bottom of the gas pass 1. Cleaningparticles falling in the pass 1 adjacent the pass 8 are directed towardsthe hoppers '7 by the inwardly inclined baflle 38. The baflle 38 alsodeflects the flow of gases towards the hoppers 7 before the gases canpass to the gas pass 8 and consequently the turning of the gases aroundthe lower edge of the baflle 38 eifects the separation of cleaningparticles from the gas stream.

The cleaning particles pass through the restricted particle outlets 2.0at the bottoms of the respective hoppers 7 and downwardly through thecollector means 13. Owing to the pressure of the gases in the gas pass 1being below atmospheric, air is drawn upwardly through the restrictedparticle outlet in opposition to the downward cleaning particle flow asis shown in FIGURE 1 by the arrows 19 by way of the adjustable airintake 14 as shown by the arrow 18 and exerts a winnowing effect on thecleaning particles tending .to prevent the entry of dust and smallparticles of deposit into the collector means 13. In the collector means13 the cleaning particles continue downwardly through the main screens25 or auxiliary screens 24 where large bodies or fragments of deposittoo long to enter the mixing nozzles 29 are retained, to the bottomoutlet 27. From the bottom outlets 27 the cleaning particles passthrough the casings of the associated cut-off valve 28 to thecorresponding mixing means 29 for entrainment in the gaseous conveyingmedium.

With the arrangement of collector means 13 and cutoif valve 28disclosed, in the event of the main screen 25 becoming choked, cleaningparticles will pass by way of the by-pass 23 and auxiliary screen 24 tothe bottom outlet 27'. In the event of the outlet 27 becoming choked, itmay be cleared by means of the poker 27 through oscillation of thepivoted arm supporting the cup-like member 28.

After being entrained in gaseous carrier medium the cleaning particlesare conveyed upwardly through the tubes 32 and 34 as shown in FIGURES 1and 2 by the arrows 35 and 36 and are discharged from the upper ends ofthe tubes 34 into the separating chamber 44. The cleaning particles aredirected from. thetubes 34 into the associated pockets 40 towards theimpact plates 42 where some of the cleaning particles rebound into'theoncoming stream. As is shown by the arrows 65, the particle flow isreversed and the cleaning particles fall to the sloping floor 46 of theseparating chamber 44 where they are stored, building up to the level 64just below the uppermost parts of the tubes 34 within the separatingchamber.

The conveying air undergoes a double flow reversal within the separatingchamber 44 and is discharged upwardly so that cleaning particles do nottend to be carried away in the gas stream through the passage 47. Theconveying medium is discharged downwardly from the passage 47 into thegas pass 8 so that any particles retained in the gas stream tend to fallthrough the pass 8 and are retained in the system.

During the cleaning operation, the conveying means are maintained inoperation so that the length of the cleaning operation may, if desired,be prolonged by the return of cleaning particles accumulating at thecollector means 13 to the separating chamber 44. Termination of thecleaning operation is efiected by closure ofthe power operating cut-01fvalve 53 and the operation of the conveying means is continued until thestorage hopper of the separating chamber has been recharged when thesupply of conveying medium to the mixing nozzles 27 is ceased and thecut-E valves 28 are closed.

The rate of discharge of the scattering means 59 is independent of therate at which the conveying means are capable of returning particlescollected at the bottom of the pass and the rate of discharge is verymuch greater than would be practicable in a system depending uponcontinuous circulation of the particles. Consequently the much denserdischarge reduces the tendency for cleaning particles to be lost byadherence to the deposits on the tubes and effective dislodgement ofdeposits is more easily obtained. By way of example, the storage hoppermay contain a charge of two tons of particles, suitably in the form ofsteel shot or pellets, which are discharged at a flow rate ofapproximately 45,000 pounds per hour and distributed to six scatteringmeans each adapted to distribute the particles over a circle at the toptube row of the uppermost tube bank having a diameter of feet.

Furthermore, the arrangement disclosed permits the replenishment ofcleaning particles to the system at a single location, suitably at thedistributing'means 53 by way of the chute 50. The use of a single hopperfeeding distributor means permits the maintenance of a uniform rate ofdischarge of cleaning particles from the various scattering means andthe drifting of particles within the gas pass from one recirculationsystem to another is avoided. A uniform distribution of cleaningparticles across the gas pass occurs and consequently a uniform cleaningefiect is obtained.

It has been found that with such method of operation, the cleaningeflEeot is highly effective and the risk of loss of particles isavoided. It is thought that the action may depend partly upon thecleaning action of material dislodged from the tubes, dislodgment beingensured by the denseness of the particle discharge and also partly bythe increased flow rate and turbulence within the tube bank created bythe flow, not only of the gases but also of the particles and thedislodged material. However this may be, an efiicient and reliablecleaning action is ensured.

While in accordance with the provisions of the statutes I haveillustrated and described herein the best form and mode of operation ofthe invention now known to me, those skilled in the art will understandthat changes may be made in the form of the apparatus disclosed withoutdeparting from the spirit of the invention covered by my claims, andthat certain features of my invention may sometimes be used to advantagewithout a corresponding use-of other features.

What is claimed is:

1. Apparatus for cleaning the surfaces of heat exchange elements in anupright gas-pass including a plurality of solid cleaning particlescattering means spaced from one another and positioned above the heatexchange elements in particle distributing relation with respectthereto, a plurality of collecting means for collecting the particles ata position below said gas pass, separate fluid lift means for conveyingsaid particles from each of the collecting means to an elevation abovesaid scattering means, a common storage hopper means arranged to receivethe particles from the conveying means, separating means in the upperportion of said hopper means for separating the particles from theconveying fluid and discharging the separated particles into the lowerportion of said hopper, a conduit connecting said hopper means and eachof said scattering means for gravitational movement of particlestherethrough, and means for controlling flow of particles from saidhopper means.

2. Apparatus as claimed in claim 1 wherein the hopper means comprise asingle hopper arranged to discharge to a distributor from whichrespective tubes for the conveyance of particles lead to the scatteringmeans.

3. Apparatus as claimed in claim 2, wherein the distributor includes achamber in which is located a cut-off valve for regulating the flow ofparticles from the hopper into the chamber. 7

4. Apparatus as claimed in claim 1, wherein the separating means forseparating particles from the gaseous conveying medium discharge througheach fluid lift means are disposed Within the storage hopper means.

5. Apparatus as claimed in claim 4, wherein a duct for the discharge ofseparated gaseous conveying medium from the separating means in saidhopper discharges downwardly into a space from which particles may tallto said collecting means and which is in communication with an induceddraft.

6. Apparatus as claimed in claim 1, wherein each of said fluid liftmeans includes an upwardly inclined venturi section having a conveyingfluid inlet, and means for introducing cleaning particles into saidventurl section.

7. Apparatus as claimed in claim 1, wherein each of said collectingmeans has a bottom outlet for cleaning particles; a spout opening fromsaid outlet and projecting into the casing of a cut-off valve, saidcut-01f valve including a cup-like member mounted on a pivoted arm toengage the end of said spout in closing relationship therewith.

References Cited in the file of this patent UNITED STATES PATENTS1,532,390 Earle Apr. 7, 1925 2,689,112 Gilmore Sept. 14, 1954 2,792,316Broman May 14, 1957 2,809,018 Broman Oct. 8, 1957 FOREIGN PATENTS745,556 Great Britain Feb. 25, 1956 753,851 Great Britain Aug. 1, 1956

